Catalyst material and a process for its preparation

ABSTRACT

A powdered catalyst material based on aluminum oxide, which contains at least one basic metal oxide and at least one noble metal from the platinum group of the Periodic System of Elements in addition to aluminum oxide. The catalyst material is obtainable by loading a support material already stabilized by basic oxides by renewed impregnation with further basic oxides. After drying and calcining this post-impregnated material at temperatures below 800° C., the catalytically active noble metals are also incorporated into the support material by impregnation.

FIELD OF THE INVENTION

[0001] The invention provides a powdered catalyst material based onaluminum oxide, which contains at least one basic metal oxide and atleast one noble metal from the platinum group of the Periodic System ofElements, as well as aluminum oxide. The catalyst according to theinvention has outstanding thermal stability with a high surface area anda high, aging-stable dispersion of the catalytically active components.It is particularly suitable for the production of catalysts for thetreatment of exhaust gases from internal combustion engines.

BACKGROUND OF THE INVENTION

[0002] Aluminum oxide is frequently used as a support material for thecatalytically active elements from the platinum group. It is obtainablein so-called high surface area modifications on whose surface the noblemetals from the platinum group can be deposited in a high dispersion.

[0003] High surface area materials in the context of this invention arematerials with a specific surface area of more than 10 m²/g, determinedby evaluating nitrogen adsorption isotherms in accordance with DIN66132. Aluminum oxides which satisfy this condition are called activealuminum oxides. These include chi, kappa, gamma, delta, theta and etaaluminum oxide (see Ullmann's Encyclopedia of Industrial Chemistry, vol.Al, 561-562, 1985, which is incorporated herein by reference in itsentirety).

[0004] For optimum use of the catalytic activity of the expensiveplatinum group metals, they have to be deposited in a very highdispersion on the support material. Efforts are made to producecrystallite sizes for the noble metals of between 1 and 10 nm on thesurface of the support material. The noble metals are deposited, forexample, by impregnating the support material with aqueous solutions ofprecursor compounds of the noble metals. Then the impregnated materialis dried and calcined to decompose the noble metal compounds, optionallyunder reducing conditions.

[0005] Four properties of the catalyst material obtained in this way areimportant for later use in catalytic processes:

[0006] a) the surface area of the material, measured as the specific BETsurface area according to DIN 66132;

[0007] b) the resistance of the crystallographic structure and surfacearea of the support material to stresses which occur during thecatalytic process, in particular to high temperatures;

[0008] c) the dispersion of the catalytically active components on thesurface area of the support material;

[0009] d) the resistance of the dispersion of catalytically activecomponents to stresses which occur during the catalytic process, inparticular to high temperatures.

[0010] In order to stabilize the crystallographic structure and thesurface area of the aluminum oxide used as support material, this isfrequently doped with basic metal oxides such as, for example, bariumoxide and lanthanum oxide, cerium oxide, or other rare earth oxides ormixtures of these oxides. This results in a slowing of the conversioninto thermally stable, but low surface area, alpha aluminum oxide. Theamount of doping components required for this purpose is 1 to 10 wt. %,with respect to the total weight of doped aluminum oxide.

[0011] U.S. Pat. No. 3,867,312 describes the preparation of a supportmaterial based on aluminum oxide which contains oxides of thelanthanides uniformly distributed in the support material. This slowsdown phase conversion of the aluminum oxide. The lanthanide oxides maybe present in the support material in concentrations of 1 to 45 wt. %,with respect to the aluminum oxide. The support material is obtained,for example, by melting lanthanum acetate and aluminum nitrate togetherby heating and by converting these into the oxides by increasing thetemperature further to 600° C. This patent is incorporated herein byreference in its entirety.

[0012] U.S. Pat. No. 4,170,573 describes a catalyst material in the formof a support material consisting of cerium oxide, lanthanum oxide andaluminum oxide, onto which platinum group metals are deposited. Toprepare the support material, active aluminum oxide is impregnated witha solution of lanthanum nitrate, dried and calcined for one hour at abed temperature between 1223 and 1253° C. Then the material isimpregnated with an aqueous solution of cerium nitrate in a similar way,dried and calcined. The catalytically active noble metals are depositedonto this support material using ammonium/sulfito complexes of thesemetals. The surface area of the materials prepared in this way is lessthan 50 m²/g. This patent is incorporated herein by reference in itsentirety.

[0013] EP 0 170 841 μl describes a catalyst which has 1 to 10 wt. % oflanthanum oxide as stabilizer, 1 to 20 wt. % of cerium oxide aspromoter, at least 0.5 to 5 wt. % of an alkali metal oxide as promoter,and one or more platinum group metals on an aluminum oxide supportmaterial. Lanthanum oxide and the promoters are incorporated in thesupport material which is present in the form of pellets byimpregnation. After impregnating the pellets with a salt of lanthanum,the support is calcined at temperatures between 800 and 1100° C. inorder to convert the salt into lanthanum oxide and for thermalstabilization purposes. This patent is incorporated herein by referencein its entirety.

[0014] EP 0 171 640 A2 describes a catalyst which contains a compositematerial consisting of aluminum oxide, lanthanum oxide, cerium oxide andat least one platinum group metal. Lanthanum and cerium are introducedinto the aluminum oxide in sequence by impregnating with lanthanumnitrate and cerium nitrate, and are then converted into the oxides bycalcining at a temperature of at least 983° C. The resulting materialhas a surface area of less than 50 m²/g. This patent is incorporatedherein by reference in its entirety.

[0015] Another process for preparing a thermally stable support materialbased on aluminum oxide is the solgel process. This process provides ahomogeneous distribution of aluminum and rare earths, at the atomiclevel, by the co-precipitation of oxidic aerogels of aluminum and rareearths. These materials have a constant ratio by weight of aluminumoxide to rare earth oxide over the entire volume of the solid material.The highly dispersed composite material obtained is then stabilized bycalcination. The surface areas which can be produced using this process,with good thermal stability, are substantially higher than thoseachieved by the previously described impregnation method. Typical valuesare 100 to 300 m²/g.

[0016] The properties of the known processes for preparing a stabilizedsupport material based on aluminum oxide are thus characterized asfollows:

[0017] In order to stabilize aluminum oxide by impregnation with, forexample, lanthanum oxide, the impregnated material has to be calcined attemperatures of more than 800° C. in order to enable diffusion oflanthanum into the inner depths of the particles of aluminum oxide, andincorporation into the crystal lattice of aluminum oxide. The resultingmaterial generally has a surface area of less than 50 m²/g and asubstantially homogeneous distribution of doping element over the crosssection of the aluminum oxide particles.

[0018] Preparing a stabilized support material based on aluminum oxideby co-precipitation provides a support material with a substantiallyhigher surface area than when using the impregnation methods. The dopingelement is distributed very homogeneously over the cross section of thesupport particles.

[0019] The catalytically active components are mostly applied to thesestabilized support materials by impregnation. It is important here toproduce a high dispersion of the catalytically active components, whichare very stable even under high thermal stresses. This is not alwaysguaranteed with known support materials. In particular, grainenlargement due to diffusion of the particles to the surface, andaggregation of these, is frequently observed, so the catalytic activityof these materials is reduced by high temperatures.

[0020] Thus, the object of the present invention is to provide acatalyst material based on aluminum oxide which has a high surface areaand a high dispersion of catalytically active components. The thermalstability of the surface area of the support material and of thedispersion of catalytically active components is intended to be betterthan those of traditional materials. Another object of the invention isthe method of preparing the catalyst material according to theinvention.

SUMMARY OF THE INVENTION

[0021] These objects are achieved by a powdered catalyst material basedon aluminum oxide which contains aluminum oxide, at least one basicmetal oxide and, as catalytically active components, at least one noblemetal from the platinum group of the Periodic System of Elements,wherein aluminum oxide and the basic metal oxides form a compositematerial which acts as support material for the catalytically activecomponents. The catalyst material is obtainable by the following processsteps:

[0022] a) provision of a powdered aluminum oxide stabilized with basicoxides as support material, which has a specific surface area of morethan 80 m²/g,

[0023] b) impregnation of the support material with a solution of atleast one precursor compound of alkaline earth and rare earth metals,

[0024] c) drying of the impregnated support material and calcination attemperatures below 800° C.,

[0025] d) repetition of process steps b) and c) until the desiredloading with basic oxides is achieved,

[0026] e) renewed impregnation of the material obtained with a solutionof precursor compounds of the catalytically active noble metals, and

[0027] f) finally drying and calcining.

[0028] The catalyst material according to the invention is thus obtainedby subsequent re-impregnation of a support material already stabilizedby basic oxides with precursor compounds of basic oxides.

[0029] The expression “stabilized aluminum oxide” in the context of thisinvention is understood to be a material disclosed in the prior art, thecrystallographic structure and specific surface area of which have beenstabilized against high temperatures by doping with basic oxides. Thisis preferably an active aluminum oxide doped with 1 to 10 wt. % oflanthanum oxide. As explained at the beginning, such a material can beobtained by impregnating with precursors of basic oxides followed bycalcining at temperatures above 800° C. The material obtained in thisway is characterized by a substantially homogeneous distribution ofdoping elements over the cross section of the powder particles.Alternatively, these materials may also be obtained by aco-precipitation process. These materials are also characterized by ahomogeneous distribution of doping elements over the cross section ofthe powder particles. Due to the requirement that the surface area be atleast 80 m²/g, the stabilized aluminum oxides obtained byco-precipitation are most suitable as starting materials for thecatalyst material according to the invention.

[0030] For the post-impregnation procedure in process step b), aqueousimpregnation solutions are preferably used, but organic solutions mayalso be used. After impregnation in step b), the material is dried at anelevated temperature of, for example, 100 to 200° C., and calcined atbelow 800° C. in order to convert the precursor compounds into basicoxides. The objective of this calcination step is to convert theprecursor compounds into the corresponding oxides, and not forcedthermal diffusion of the doping elements into the aluminum oxidelattice. Therefore, temperatures of less than 700° C. are preferablyused. The appropriate calcination temperature depends on the precursorcompounds used and may be lowered to, for example, 600 to 500° C. whenusing nitrates.

[0031] According to current understanding of the invention, an elevatedconcentration of basic oxides is produced at the surface of the supportmaterial by means of this action. These basic oxides lead to an elevatedconcentration of hydroxyl groups at the surface which are used asdocking points for the precursor compounds of catalytically active noblemetals subsequently applied in process step d), and lead to stableanchorage of the noble metal particles on the surface after subsequentcalcination in process step e). The result of this step is a catalystmaterial with high thermal stability of the support and a highdispersion of catalytically active noble metals and very good aging andthermal stability of this dispersion, due to reduced mobility of thenoble metal particles on the surface of the support.

[0032] The catalyst material according to the invention has a specificBET surface area, measured in accordance with DIN 66132, of more than 80m²/g. The total pore volume is preferably between 0.3 and 0.9 ml/g.

[0033] The stabilized aluminum oxide provided in step a) may have thevarious crystal structures of the transition oxides of aluminum oxide.In order to stabilize these characteristics, the aluminum oxide containsbasic oxides, preferably in concentrations between 0.5 and 20 wt. %,with respect to the total weight of stabilized aluminum oxide or supportmaterial.

[0034] Due to subsequent impregnation, additional basic oxides aredeposited, preferably at a concentration of 5 to 15 wt. %, with respectto the total weight of support material, so that the total concentrationof basic oxides in the support material is 1 to 35 wt. %.

[0035] Different basic oxides may be combined in the catalyst materialaccording to the invention, that is, the basic oxides used to stabilizethe starting material do not have to be identical to the oxidesdeposited on the support material in process steps b) and c).

[0036] The catalyst material according to the invention is preferablystabilized and doped with basic oxides from the alkaline earth and rareearth oxides, in particular with oxides of the elements magnesium,calcium, strontium, barium, lanthanum, cerium, praseodymium, neodymium,samarium, europium, terbium and ytterbium. These oxides may be presentindividually or as a mixture. Stabilization and doping of the aluminumoxide with oxides of lanthanum, cerium, or mixtures thereof, isespecially advantageous.

[0037] Suitable precursors of the basic oxides are any soluble compoundsof the alkaline earth and rare earth metals. These include solubleorganic complex compounds, acetates, nitrates and chlorides. Organiccomplex compounds, acetates and nitrates, which are deposited onto thetreated support material using a known impregnation process, arepreferably used. The pore volume impregnation method, in which theprecursor compounds are dissolved in a volume of solvent whichcorresponds to about 60 to 110% of the absorption capacity of theinitially introduced support material, is preferably used. If thesolubility of the precursor compound is not sufficiently high to applythe desired amount in one step, then the impregnation procedure may berepeated several times, until the desired amount has been deposited onthe support material.

[0038] To apply the catalytically active noble metals, knownimpregnation techniques may also be used, wherein the pore volumeimpregnation method is also preferred for the noble metals. According tothe invention, metals from the platinum group are used as noble metals,in particular platinum, palladium, rhodium and iridium, which may bedeposited individually or in various combinations and mixing ratios atconcentrations of 0.01 to 5 wt. %, with respect to the total weight ofcatalyst material.

[0039] As explained above, the catalyst material according to theinvention has an elevated concentration of basic oxides at the surface.Tests using secondary ion mass spectrometry (SIMS) have shown that, inparticular in an outer edge zone with a thickness of less than 100atomic layers, the concentration of the metals forming the basic oxides,relative to aluminum, is at least 20% greater than at a depth with athickness of more than 100 atom layers.

[0040] Accordingly, the invention also provides a powdered catalystmaterial based on aluminum oxide which contains at least one basic metaloxide and, as catalytically active components, at least one noble metalfrom the platinum group in the Periodic System of Elements in additionto aluminum oxide, wherein aluminum oxide and the basic metal oxidesform a composite material which acts as a support material for thecatalytically active components, characterized in that the catalystmaterial has a specific surface area of more than 80 m²/g, and the ratioof the SIMS intensities of the metals forming the basic metal oxides toaluminum at the surface of the powder particles is at least 20% greaterthan at a depth of more than 100 atomic layers from the surface of theparticles.

[0041] Considerations governing the choice of basic oxides,catalytically active noble metals, and concentrations, are the same asthose mentioned above. In particular, the catalyst material has a totalconcentration of basic oxides of between 1 and 35 wt. %, with respect tothe total weight of catalyst material.

[0042] Enrichment of the basic oxides at the surface of the supportmaterial increases the concentration of hydroxyl groups at the surfaceof the particles and these are used as docking points for the precursorcompounds of platinum group metals when depositing the catalyticallyactive platinum group metals. The increased functionalization of thesurface leads to a very high dispersion of deposited noble metals, andalso improves anchorage of the deposited noble metal crystallites on thesurface, so that the risk of neighboring crystallites aggregating due toincreased mobility at high temperatures is reduced.

[0043] Surface enrichment of the basic oxides in accordance with theinvention is substantially restricted to a very thin edge zone with athickness of a few atomic diameters. The variation in concentration ofelements in the edge zone can be measured using secondary ion massspectrometry (SIMS). The application of secondary ion mass spectrometryto investigating the surfaces of powders is described in “SIMS/XPS Studyon the Deactivation and Reactivation of BMFI Catalysts Used in the VaporPhase Beckmann Rearrangement” by P. Albers et al. Journal of Catalysis,vol. 176, 1998, 561-568, which is incorporated herein by reference inits entirety.

[0044] The measurements are performed as follows: the loose powder isintroduced, in a sample holder, into the measurement chamber of a massspectrometer, and this is evacuated down to a pressure of 10⁻⁸ to 10⁻⁹mbar. Then the powder surface is bombarded with 5 keV argon ions, withsimultaneous charge compensation, so that the outer atoms are strippedoff, layer by layer. The secondary ions emitted during this process areanalyzed. Their distribution with respect to each other corresponds tothe distribution of the corresponding elements in the surface of thesample. To normalize the experimental values, the ratios of the measuredintensities of secondary ions to the intensity of aluminum ions arecalculated. This procedure provides a picture of the distribution ofelements as a function of the depth of abrasion relative to the mainelement in the support material.

[0045] The area measured, that is, the surface of powder bombarded withargon ions is 4×4 mm², and is thus many times greater than thecross-sectional area of the individual powder particles, which have adiameter of only between 0.1 and 50 μm. The measurement thus providesthe average distribution of elements over many powder particles. Thismeans that random results are largely excluded.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The invention is now explained in more detail using a fewexamples. The following figures are provided:

[0047]FIG. 1: SIMS depth profile of lanthanum for support material 1;

[0048]FIG. 2: SIMS depth profile of lanthanum for support material 2;

[0049]FIG. 3: SIMS depth profile of lanthanum for support material 3

[0050]FIG. 4: Temperature at which a 50% conversion of hydrocarbons (HC)and carbon monoxide (CO) is achieved for catalysts in examples 1 to 3with a normalized air to fuel ratio of 0.999 and periodic modulation ofthe air/fuel ratio A/F by ±0.5 at a frequency of 1 Hz (1 Hz; ±0.5 A/F);

[0051]FIG. 5: Temperature at which a 50% conversion of hydrocarbons (HC)and carbon monoxide (CO) is achieved for catalysts in examples 1 to 3with a normalized air to fuel ratio of 1.05 (static, with no modulationof A/F);

[0052]FIG. 6: Temperature at which a 50% conversion of hydrocarbons (HC)and carbon monoxide (CO) is achieved for catalysts in examples 1 to 3with a normalized air to fuel ratio of 1.1 (static, with no modulationof A/F).

DETAILED DESCRIPTION OF THE INVENTION

[0053] The following support materials were used or prepared to producecar exhaust gas catalysts using catalyst materials according to theinvention:

[0054] Support Material 1:

[0055] A commercially available aluminum oxide stabilized with 3 wt. %of lanthanum oxide with a BET surface area in the freshly calcined stateof 143 ml/g is used as support material 1.

[0056] Support Material 2:

[0057] To prepare support material 2, 2000 g of support material 1 wereimpregnated with 856 g of a lanthanum ethylene diamine tetra acetatesolution with a lanthanum content of 2.4 wt. %, using the pore volumeimpregnation method. The impregnation solution had a pH of 5. The powderobtained in this way was then dried for 12 hours at 120° C. and thencalcined for 1 hour at 750° C. in air. Due to this subsequentimpregnation, an additional 1 wt. % of lanthanum oxide was deposited onthe support material, so that the total concentration of lanthanum oxidein the support material was 4 wt. %.

[0058] The specific surface area of the material decreased from 143 m²/gto 131 m²/g due to the subsequent impregnation procedure.

[0059] Support Material 3:

[0060] To prepare support material 3, 2000 g of support material 1 wereimpregnated with 856 g of a lanthanum nitrate solution with a lanthanumoxide content of 16 wt. %, using the pore volume impregnation method.The impregnation solution had a pH of 4. The powder obtained in this waywas then dried for 12 hours at 120° C. and then calcined for 1 hour at500° C. in air.

[0061] Due to this subsequent impregnation, an additional 7 wt. % oflanthanum oxide was deposited on the support material, so that the totalconcentration of lanthanum oxide in the support material was 10 wt. %.The specific surface area of the material decreased from 143 m²/g to 123m²/g.

[0062] SIMS depth profiles were determined for lanthanum and aluminum inthe three support materials, using the method described above. FIGS. 1to 3 show the SIMS spectra for lanthanum as a function of the time ofbombardment of the sample surface with argon ions, in three-dimensionalimages. Each spectrum corresponds to a specific abraded depth. The lastspectrum in these images corresponds to an abraded depth of about 100atomic layers.

[0063] The depth profile for support material 1 shows a reducedlanthanum concentration at the surface, but this changes to a constantconcentration, with increasing depth of abrasion. The depth profiles forthe support materials prepared according to the invention, on the otherhand, show a clearly increased lanthanum concentration in an edge zoneof a few atomic layers, which falls away to a constant value withincreasing depth of abrasion.

[0064] Table 1 gives the ratio of SIMS intensities determined foraluminum to the intensities determined for lanthanum for three differentdepths of abrasion, initially (at the surface), in the middle, and atthe end of the test. TABLE 1 Quotients of SIMS intensities for Al/La.Site of Support measurement material 1 Support material 2 Supportmaterial 3 Start 70.8 63.8 17.9 Middle 69.7 101 19.4 End 75.1 113 24.0

[0065] As shown by these results, the Al/La ratio changes, in supportmaterials 2 and 3 prepared according to the invention, by a factor of 2from the surface to a depth of about 100 atomic layers. Accordingly, theconcentration of lanthanum is enriched at the surface of the particlesof support material.

[0066] Car exhaust gas catalysts were prepared using support materials 1to 3, and their light off temperatures for the conversion ofhydrocarbons and carbon monoxide were determined. The catalysts wereintended for use as start catalysts located close to the engine andwhich are subjected to very high temperatures during operation. Thesupport structures for all the catalysts were honeycomb structures madeof cordierite with a volume of 0.3 l and a cell density of 46.5 cm⁻².

EXAMPLE 1

[0067]120 g of support material 1 were mixed with 20 g of acerium/zirconium mixed oxide (70 wt. % cerium oxide and 30 wt. %zirconium oxide with a BET surface area in the freshly calcined state of87 m²/g) impregnated with 0.7 g of platinum and 3.2 g of palladium usingthe pore volume impregnation method. The impregnated mixture was thendried and calcined at 500° C. in air.

[0068] This powder was stirred with water to give an aqueous suspensionand milled to a particle size of 3 to 5 μm (d₅₀). The oxidic solids inthe dispersion were applied to one of the support structures provided,using an immersion method. The loading concentration was 160 g ofcatalyst material per liter of honeycomb structure volume.

EXAMPLE 2

[0069] A catalyst was prepared using the same method as described inexample 1, but using support material 2.

EXAMPLE 3

[0070] A catalyst was prepared using the same method as described inexample 1, but using support material 3.

APPLICATION EXAMPLE

[0071] All the catalysts were aged for 4 hours at 1100° C. in anatmosphere consisting of 88 vol.% nitrogen, 10 vol.% water and 2 vol.%oxygen before measuring the light off temperatures in the engine.

[0072] The light off temperatures were measured in a 2 l petrol engine.For this purpose, the catalysts were increasingly heated with normalizedair to fuel ratios of 0.999 (1 Hz 0. 5 A/F) and 1.05 (static) or 1.1(static) and subjected to a space velocity of 206000 h⁻¹. During theheating process, the conversions of hydrocarbons and carbon monoxidewere determined as a function of the temperature. The temperatures for aconversion of 50% for each of the harmful substances were determinedfrom these measurements for the individual catalysts.

[0073] The results determined are shown graphically in FIGS. 4 to 6. Ascan be seen from these results, the catalysts in examples 2 and 3 whichwere prepared using support materials according to the invention arecharacterized by a substantially reduced light off temperature,although, due to the subsequent impregnation procedure, the specificsurface area of the support materials was less than the specific surfacearea of the support material used in example 1.

[0074] Further variations and modifications of the foregoing will beapparent to those skilled in the art and are intended to be encompassedby the claims appended hereto.

[0075] German priority application 199 08 394.0 is relied on andincorporated herein by reference.

We claim:
 1. A powdered catalyst material of aluminum oxide, at leastone basic metal oxide, and at least one catalytically active noblemetal, wherein aluminum oxide and the at least one basic metal oxideform a support material for the at least one catalytically activecomponent, the powdered catalyst material obtained by a processcomprising: a) providing as a support material a powdered aluminum oxidestabilized with at least one basic oxide, and having a specific surfacearea greater than 80 m²/g; b) impregnating the support material with asolution of at least one precursor compound of a member selected fromthe group consisting of at least one alkaline earth metal and at leastone rare earth metal; c) drying the resulting impregnated supportmaterial; and d) calcining the resulting dried impregnated supportmaterial at a temperature below 800° C.; e) repeating process steps b)through d) until a desired loading with basic oxides is achieved; and f)impregnating the resulting calcined impregnated support material with asolution of at least one precursor compound of at least onecatalytically active noble metal; g) drying the resulting furtherimpregnated support material; and h) calcining the resulting driedimpregnated support material to obtain the powdered catalyst materialproduct.
 2. The catalyst material according to claim 1, wherein thepowdered aluminum oxide support material provided has a concentration ofbasic oxides in step a) of from 0.5 to 20 wt %, with respect to thetotal weight of support material.
 3. The catalyst material according toclaim 2, wherein the concentration of the member selected from the groupconsisting of at least one alkaline earth metal and at least one rareearth metal incorporated into the support material by impregnation instep b) is from 0.5 to 15 wt. %, with respect to the total weight ofsupport material.
 4. The catalyst material according to claim 1, whereinthe at least one basic oxide of step a) is selected from the groupconsisting of alkaline earth oxides and rare earth oxides.
 5. Thecatalyst material according to claim 4, wherein the at least one basicoxide is at least one member selected from the group consisting oflanthanum oxide and cerium oxide.
 6. The catalyst material according toclaim 1, wherein the at least one catalytically active noble metal is atleast one member selected from the group consisting of platinum,palladium, rhodium, iridium, and mixtures thereof, which are present ina concentration of from 0.01 to 5 wt. %, with respect to the totalweight of catalyst material.
 7. A powdered catalyst material comprisingaluminum oxide, at least one basic metal oxide, and at least onecatalytically active noble metal, wherein the aluminum oxide and the atleast one basic metal oxide form a composite support material forcatalytically active components, wherein the catalyst material has aspecific surface area of more than 80 m²/g, wherein a ratio of SIMSintensities of the basic metal oxides to SIMS intensities of thealuminum, at the surface of the powder particles, is at least 20%greater than that at a depth of more than 100 atomic layers from thesurface of the particles.
 8. The catalyst material according to claim 7,wherein the at least one basic metal oxide is at least one memberselected from the group consisting of alkaline earth oxides and rareearth oxides.
 9. The catalyst material according to claim 8, wherein theat least one basic metal oxide is at least one member selected from thegroup consisting of lanthanum oxide and cerium oxide.
 10. The catalystmaterial according to claim 9, wherein the at least one basic metaloxide is present in a concentration, with respect to the total weight ofthe catalyst material, of between 1 and 35 wt. %.
 11. The catalystmaterial according to claim 10, wherein the at least one noble metal isat least one member selected from the group consisting of platinum,palladium, rhodium, iridium, and mixtures thereof and is present in aconcentration of 0 01 to 5 wt %, with respect to the total weight of thecatalyst material.
 12. A process for preparing a powdered catalystmaterial, comprising: a) providing as support material a powderedaluminum oxide stabilized with at least one basic oxide, and having aspecific surface area greater than 80 m²/g; b) impregnating the supportmaterial with a solution of at least one precursor compound of at leastone member selected from the group consisting of an alkaline earth metaland a rare earth metal; c) drying the resulting impregnated supportmaterial, and, d) calcining the dried support material at a temperaturebelow 800° C.; e) repeating steps b) through d) until a desired loadingwith the at least one basic oxide is achieved; and f) impregnation ofthe loaded support material with a solution of at least one precursorcompound of the at least one catalytically active noble metal; and, g)final drying and calcining to obtain the powdered catalyst materialproduct.
 13. The process according to claim 12, wherein the stabilizedaluminum oxide provided as support material in step a) has aconcentration of 1 to 20 wt. % of the at least one basic oxide.
 14. Aprocess according to claim 13, wherein the at least one member selectedfrom the group consisting of an alkaline earth metal and a rare earthmetal additionally incorporated into the support material in step b)amounts to 0.5 to 15 wt. %, with respect to the total weight of supportmaterial.
 15. A powdered support material of aluminum oxide, at leastone basic metal oxide, and at least one noble metal, obtained by aprocess comprising: a) providing as support material a powdered aluminumoxide stabilized with at least one basic oxide, and having a a specificsurface area of more than 80 m²/g; b) impregnating the support materialwith a solution of at least one precursor compound of at least onemember selected from the group consisting of an alkaline earth metal anda rare earth metal; c) drying the impregnated support material; and d)calcining the dried support material at a temperature below 800° C.;and, e) repeating process steps b) through d) until a desired loadingwith the at least one basic oxide is achieved.